In plural paths between two nodes, the transmission side dispersively inputs traffics to respective paths and the reception side reintegrates them from the respective paths. Thus, a higher transfer rate can be obtained in principle, compared with the case where a single path is used. This mechanism relates to a technique of combining paths to construct one logical path. Typically, Inverse Multiplexing is cited, which is utilized to obtain a logical broad band line from plural low rate links. As applications to data communications, there are multiplexing of ATM line and Multilink PPP being a multiplex protocol for PPP links.
As a traffic distribution scheme, typified by Inverse Multiplexing, of forming one logical path by combining paths, the round robin scheme, for example, of transmitting packets or fragments in turn to respective paths has been broadly used (refer to non-Patent document 1). This method is effective when the rate (or speed) in each path is nearly the same and constant. However, the problem is that when the rates between paths are in imbalance, the transfer rate between nodes is rate-controlled to the slowest path.
In order to deal with such a problem, the weighted round robin is known for controlling the use frequency of each path according to the rate. The round robin is installed to router products corresponding to the technique of combining paths to form one logical path. The product manufactured by Cisco employs the method of implementing optimum load distribution by hashing input packets to determine the output path. These sets of information are described in the documents published by companies (for example, non-Patent document 2).
Any one of the above-mentioned well-known techniques assumes that each path consists of a cable link only.
As to the technique, which combines paths to construct one logical path, the path containing a radio link is proposed. In this proposed scheme, the input packet is divided into fragments to allocate them to each path but the ratio of each fragment size is changed according to only the rate of each path in transmission (for example, non-Patent document 3 and Patent document 6).
In the plural path selectable communications system, the technique has been proposed of monitoring the status of each path and selecting a path, in consideration of the path status or the delay time. (For example, refer to Patent document 1, Patent document 2, Patent document 3, Patent document 4, and Patent document 5)    Patent document 1: Japanese Patent laid-open publication No. 2000-49862    Patent document 2: Japanese Patent laid-open publication No. 2001-308917    Patent document 3: Japanese Patent laid-open publication No. 2001-333100    Patent document 4: Japanese Patent laid-open publication No. 2002-176441    Patent document 5: Japanese Patent laid-open publication No. 58-27449    Patent document 6: Japanese Patent laid-open publication No. 2000-216815    Non-Patent document 1: “Stripping Within the Network Subsystem”, IEEE Network, July/August, 1995    Non-Patent document 2: Cisco Systems “Load Balancing with Cisco Express Forwarding”, Cisco Application Note, January 1998    Non-patent document 3: “Adaptive Inverse Multiplexing for Wide-Area Wireless Networks”, Snoeren et al, Proceedings of IEEE GlobeCom, December 1999